Taxonomic Characterization: Total lack of external eyes and of melanin pigment. Muzzle
spatulate. Lack of scales. Head is long and bulb shaped with sensitive pores.
Caudal region (37-54%) longer than in other synbranchids (Navarro y Valdés,
1990).

Species Range: Cenotes and groundwater on the Yucatan Peninsula, Mexico.
O. infernale has been reported from caves in the Reserva de la Biósfera
de Sian Ka'an in Quintana Roo. This species coexists with
Typhliasina pearsei - 100% of the records where
Ophisternon was found - and the catfish Rhamdia guatemalensis -
57% of them. Very few specimens (maximum two at the same time) have been
observed in very few localities. It occurs in only about 7% of the caves
recorded. Underwater exploration should increase the number of recorded sites.

Ecology: Builds mucus-lined burrows in organic rich sediments within the
freshwater part of the aquifer. Based on few sightings, it has been observed
under the stones in muddy bottoms at the shallow parts of cave cenotes, although
Navarro y Valdés (1990) reported a sighting at a depth of 24 m. The principle
source of energy in this environment is feces from bats and swallows.
Ophisternon feeds on the stygobitic shrimp
Creaseria morleyi. It tolerates
low oxygen concentration levels and is able to breathe atmospheric oxygen (Schmitter-Soto,
1998a).

Life History: This species has been reported as oviparous (Schmitter-Soto,
1998a).

Evolutionary Origins:O. infernale appears to be clustered in
caves located along the old Pliocene shoreline (Wilkens, 1982). Although other
cavernicolous species have secondarily spread over northern Yucatan through
channels in the subterranean aquifer, both O. infernale and
Typhliasina pearsei seem to be primarily
restricted to caves and cenotes near their original sites of cave colonization (Wilkens,
1982).

Conservation Status: Endangered (Williams et al., 1989), Endangered (IUCN
1990, 1994), Endangered (criteria A1ac+2c, B1+2c) (IUCN 1996). The IUCN (1996)
criteria describe the threats which are: An observed reduction of at least 50%
over the past 10 years, or 3 generations, because of a decline in extent of
occurrence (EO), area of occupancy (AO), and/or habitat quality; together with a
similar reduction over the next 10 years for the same reason. EO less than 5000 km2 or
AO less than 500 km2 plus population known from less than 5 sites with a continuing decline in EO, AO and/or habitat quality (Medina-Gonzáles et al., 2001).The main threats to this species, and to the syntopic
Typhliasina pearsei (Bythitidae), are from
human-induced water pollution,
particularly bacterial in the form of fecal coliforms and from excess nitrate.
If their occurrence is restricted to the shallow parts of caves, they are more
exposed to human disturbance, either directly by modification and use of the
systems, or indirectly by actions on the surface of the ground, like waste and
waste water disposal. The human population obtains its water from the aquifer
underlying the plateau and, until recently, disposed of its waste water almost
directly back into the same aquifer, often only a few meters from where it was
obtained. This situation is particularly acute under the largest city, Mérida
although most of the people here, as in other urban areas use piped water, but
it seems likely that the same situation will exist elsewhere on the peninsula.
In rural areas there is little or no sewage treatment and that industrial and
domestic waste is sometimes discarded into caves. The population of the
peninsula is growing (censused at 2.9 million in 1995; Mérida estimated at
649,770 in 1995) and this will place greater and greater strain on the water
resources of the area.Wastewater in Mérida is now collected and pumped to
various treatment plants. The resulting treated product is now injected into the
saline groundwater 200 m below the surface of the aquifer. In theory, the
injected water should become saline and remain below the less dense freshwater
lens. However in practice, this is not working properly due to leakage at
shallower depths causing damage to the freshwater aquifer.Mérida is only one of many growing towns and cities on
the Yucatán Peninsula which has a growing population as well as increasing
numbers of tourists. Thus, there is a steadily increasing demand for clean water
for domestic purposes and concurrently, the necessity that resulting wastewater
be completely and rapidly removed. The continued existence of all of the
freshwater organisms of the plateau depends wholly on their water supply. Human
water supply should be augmented by the collection (and subsequent treatment) of
rainfall to supplement that obtained from the aquifer. All wastewater should be
collected and properly treated before injection into the aquifer. Detailed
studies of the aquifer need to be made to monitor its health. It is necessary to
intensively survey the occurrence of cave and groundwater species such as
Ophisternon in order to have an up to date distribution records.

Rosen, D.E. & P.H. Greenwood. 1976. A fourth neotropical species of
synbranchid eel and the phylogeny and systematics of synbranchiform
fishes. Bulletin of the American Museum of Natural History.
157(1):1-70.